The invention relates to a process for producing purified 1,1,1,3,3-pentafluorobutane (HFC-365mfc).
1,1,1,3,3-pentafluorobutane is used, for example, as a propellant in the production of foamed synthetic resins. It may be produced, for example, from the corresponding pentachlorobutane compound, hydrogen fluoride and a fluorination catalyst. 1,1,1,3,3-pentafluorobutane produced in this way can contain hydrogen chloride, hydrogen fluoride or unsaturated carbon compounds that derive from the fluorination reaction or the starting material. It is desirable to produce a purified product from this impure product. This object is achieved by the process according to the present invention.
The process according to the invention provides that purified 1,1,1,3,3-pentafluorobutane with a decreased content of HCl, HF and/or unsaturated impurities is produced from crude 1,1,1,3,3-pentafluorobutane by treating the crude 1,1,1,3,3-pentafluorobuatane in the liquid phase with a solid inorganic sorption agent or diatomic molecules which add to Cxe2x80x94C-multiple bonds and by separating the treated 1,1,1,3,3-pentafluorobutane.
Pressure and temperature are selected such that the process is carried out in the liquid phase. Preferably, the pressure is from 1 to 5 atm (abs).
Solid inorganic sorption agents can be used to separate both the acid components and also the unsaturated impurities. Diatomic molecules allow the derivatization of the unsaturated compounds to non-toxic compounds and/or compounds that can be separated by distillation.
Preferred solid inorganic sorption agents are activated carbon and sorbents composed of aluminum oxide or silicon dioxide. They are particularly well suited for separating hydrogen chloride and/or hydrogen fluoride.
The treatment with the sorption agent is advantageously carried out at a temperature from xe2x88x9230xc2x0 C. to +100xc2x0 C., preferably 15xc2x0 C. to 25xc2x0 C.
To decrease the content of unsaturated compounds, hydrogen chloride or elemental fluorine, chlorine or hydrogen is used as the preferred diatomic molecule.
One possible procedure is initially to decrease the content of unsaturated compounds by means of said diatomic molecules and subsequently to decrease further impurities by means of a solid inorganic sorption agent.
To decrease the content of unsaturated compounds, it is particularly preferred to use elemental fluorine, preferably in a mixture with an inert gas, such as nitrogen or argon. The treatment with elemental fluorine (or its mixtures with inert gas) is advantageously carried out at a temperature in the range from xe2x88x9280xc2x0 C. and +20xc2x0 C., preferably in the range from xe2x88x9220xc2x0 C. and xe2x88x9210xc2x0 C. A good effect can be observed even at a low fluorine concentration of up to 10% by volume.
Depending on the duration of the treatment or the amount of purifying agent used, the impurities can be, more or less, completely separated. For instance, if less fluorine is used than is required for attachment to the unsaturated impurities, a corresponding amount of impurities remains in the product to be purified. This can be determined, however, by simple manual experiments and product analysis. The treatment with elemental fluorine or a mixture of fluorine and inert gas is preferably continued for such a time until a 1,1,1,3,3-pentafluorobutane is obtained with a maximum content of 20 ppm of unsaturated chlorine-fluorine compounds and 10 ppm of unsaturated C2 compounds. The content of hydrogen chloride and/or hydrogen fluoride is run until a maximum of 1 ppm of each is contained. To this end, a treatment with amorphous silicon dioxide or aluminum oxide is used in particular.
If the crude product has been treated with a diatomic molecule, the separation of the resulting product into pure pentafluorobutane and other halogenated hydrocarbons can be effected by fractional condensation or, for example, also by distillation.
The process according to the invention makes it possible to produce 1,1,1,3,3-pentafluorobutane with a maximum concentration of 1 ppm of HF, 1 ppm of HCl, 10 ppm of unsaturated (chlorine) fluorine compounds and 10 ppm of unsaturated C2 compounds. Such highly pure pentafluorobutane is novel and is likewise a subject of the present invention.
The process according to the invention is outstandingly suitable for purifying 1,1,1,3,3-pentafluorobutane which is contaminated with fluorotricholoroethylene (as the only impurity or a component of impurities). It has been found that fluorotrichloroethylene is particularly difficult to separate since it is very unreactive. The process according to the invention makes it possible to decrease even this impurity to a maximum concentration of 20 ppm, and even to a concentration of less than 0.1 ppm.
Due to its low reactivity, fluorotrichloroethylene can be used as a control substance when monitoring the purification of 1,1,1,3,3-pentafluorobutane which is contaminated with fluorotrichloroethylene and further unsaturated compounds. Surprisingly it was found that only the decrease in the concentration of fluorotrichloroethylene needs to be monitored and the simultaneous monitoring of the decrease in the concentration of other unsaturated compounds may be dispensed with. Once fluorotrichloroethylene has been decreased to the desired level, other unsaturated compounds are likewise depleted. The use of fluorotrichloroethylene as a control substance when monitoring the purification of 1,1,1,3,3-pentafluorobutane, which contains fluorotrichloroethylene as well as further unsaturated compounds as impurities, is also a subject of the invention. Monitoring can be effected by means of GC-MS (SIM run=Selective Ion Mass). The detection limit for CFC1111 when determined by means of gas chromatography (GC)xe2x80x94thermal conductivity detection (t.c.d.)xe2x80x94is 100 ppm. With GC-MS in the SIM run mode (SIM run status), the detection limit is 0.1 ppm of CFC1111.
The purification process according to the invention makes it possible to produce highly pure 1,1,1,3,3-pentafluorobutane. Until now such purification operations were conducted only with highly stable fluorinated or fully halogenated compounds. Particularly the treatment with elemental fluorine produces a surprising result since, instead of the addition to the unsaturated compounds, a substitution reaction on the pentafluorobutane with formation of hexafluorobutane, heptafluorobutane or perfluorobutane would have been expected. The use according to the invention of fluorotrichloroethylene as a control substance in monitoring saves time, since it makes it possible in the recording or analysis of spectra to concentrate on the range in which fluorotrichloroethylene is registered. Working in the liquid phase saves energy.